The purpose of the study was to compare rotational and reciprocal instrumentation techniques by measuring the effectiveness of dentin removal and preserving the original root canal anatomy. Twenty permanent mandibular molars were mechanically cleaned and an access cavity preparation was made. Afterwards, a standardized X-ray of each tooth was done. The first group was instrumented with a rotational instrumentation technique, the F360 system (Komet Dental, Lemgo, Germany), and the second group was instrumented with the Endo-Eze Genius reciprocating system (Ultradent Products, Utah, USA) according to the manufacturer's protocols. X-ray images were taken after instrumentation. Measurements were then made by using computer software and statistical processing of the data obtained. Both techniques resulted in a statistically significant increase in root canal diameter at all levels except the second level of the reciprocating technique. No statistically significant difference was found between the systems at any level. Regarding the maintenance of root canal anatomy, both techniques lead to canal alignment, with a statistically significant difference present in the apical part of the tooth, with the F360 rotary system (Komet Dental, Lemgo, Germany) deviating significantly from the Endo-Eze Genius reciprocating system (Ultradent Products, Utah, USA).